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Relativity and gravitational theory Definition

M-theory

Builds on String theorySuperstring theoryEleven-dimensional supergravityBrane

Definition

M-theory is the name of the conjectured quantum theory, in eleven spacetime dimensions, characterized by the following properties.

  1. Its low-energy limit is eleven-dimensional supergravity.
  2. Compactified on a circle of radius RR, it is equivalent to type IIA superstring theory with string coupling gs=R/ℓsg_s = R / \ell_s, where ℓs\ell_s is the string length.
  3. Compactified on the interval S1/ℤ2S^1 / \Z_2, it is equivalent to the E8×E8E_8 \times E_8 heterotic string theory.
  4. It contains branes of spatial dimension 22 and 55, the M2-brane and the M5-brane. They couple electrically and magnetically to the three-form field of eleven-dimensional supergravity.

These properties do not determine a mathematical definition: no complete formulation of M-theory is known.

Remarks

Example of the circle limit at work: as gs→∞g_s \to \infty in type IIA string theory, property 2 gives R→∞R \to \infty, so the strongly coupled type IIA theory becomes eleven-dimensional. Through further dualities, the other superstring theories are also limits of M-theory, so it unifies all five. Non-example: eleven-dimensional supergravity alone is not M-theory; it is only the low-energy limit and is not a consistent quantum theory by itself. The letter M was left without a fixed meaning by Witten. The BFSS matrix model is a proposal for a nonperturbative formulation in a special frame.

Reading path

To understand this page from the ground up, read these 5 pages in order. The foundations come first.

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Each page uses the pages above it. The colour of the bar on a box shows how strong the evidence is, and the box also gives it as text. The list has the same pages.
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  1. Brane concept
  2. Eleven-dimensional supergravity concept
  3. String theory concept
  4. Superstring theory concept
  5. M-theory definition

Further reading

  1. Web https://en.wikipedia.org/wiki/M-theory
About this page
Tag9JH5VPC3VN
URIm2://9JH5VPC3VN
Kinddefinition
WritingW0 stub
MSC83E30, 81T30, 83E50
DefinesM-theory
UsesString theory, Superstring theory, Eleven-dimensional supergravity, Brane
Changed3 November 2026

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